The present invention relates to percussion musical instruments, and in particular drums. More specifically, the invention relates to a process for making a drum head membrane and the drum head membrane resulting from the process.
A variety of musical instrument drums exist such as bass drums, tympani drums, kettle drums, snare drums, tom-toms, etc. Although the various drums differ from each other in application and sound all require a battering or striking surface secured over a hollow generally cylindrical structure.
The sound generated by the particular drum results from the fundamental frequency overtones and resonance all of which are, in part, a function of vibration decay or dampening time.
The vibration decay or dampening time is determined by the structural characteristics of the drum such as the size and weight of the drum, the nature of the battering surface and the tension imposed on the battering surface.
In general, the battering surface is made of animal skin or synthetic polymer sheets held in tension. Generally the tension is applied by means such as adjustable lugs or turnbuckles secured to peripheral collars integrally formed with the drum head membrane.
One common method for producing drum head membranes from polymer sheets is a thermoforming process in which sheets of a polymer such as polyester usually 0.003 to 0.010 inch thick are placed in a mold and are subjected to the simultaneous application of heat and pressure. The resultant membrane is a flat, essentially circular surface with an integrally formed depending periphery or collar. In the formation process, heat is applied to the mold to raise the temperature of the polymer to the range of 250xc2x0 F. to facilitate deformation of the polymer to properly form the collar.
It has been found that the thermoforming process has detrimental effects on the drum head membrane. The heat causes the polyester to shrink and become brittle.
It is an object of the present invention to provide a process for the manufacture of polymer drumheads that avoids shrinkage and brittleness caused by existing processes.
It is a further object of the present invention to provide a process for the manufacture of drumheads and a resultant drumhead that is easier to tune, has a full fundamental tone and a wide range of upper partial harmonics.
To this end a new and improved mold and process is provided. The mold is comprised of a peripheral section in which heat is delivered in the range of 180xc2x0 F.-230xc2x0 F. and a central section in which a heat exchange system is located. Coolant, such as water, is delivered to the heat exchange system to maintain the temperature of the mold central surface exposed to the polymer in the range of 90xc2x0 F.-130xc2x0 F.
The process proceeds by inserting a polymer sheet between the mold sections, securing the mold sections together under pressure and applying heat to the mold. As heat is applied to the mold, coolant is circulated through the heat exchange system to maintain a relatively low temperature in the area of the membrane battering surface and at the same time deliver higher temperature heat to the peripheral collar area.